include single table inh discriminator for query.update() / query.delete()?

[Ollie Rutherfurd]

ie session.query(Subclass).update(...) updates all rows in the table vs just Subclass rows.

Script attached that demonstrates the issue. There are two rows, only one should be updated, but both are updated.

[Mike Bayer]

just had #3902 earlier today....again, this is a documented limitation:

http://docs.sqlalchemy.org/en/latest/orm/query.html?highlight=query%20update#sqlalchemy.orm.query.Query.update

The Query.update() method is a “bulk” operation, which bypasses ORM unit-of-work automation in favor of greater performance. Please read all caveats and warnings below. The polymorphic identity WHERE criteria is not included for single- or joined- table updates - this must be added manually, even for single table inheritance.

I suspect this may be a backwards compatibility issue and I'm pretty sure this could be added as an enhancement but for the moment it's not part of the usage contract and it's documented.

[Ollie Rutherfurd]

Ok, thanks -- definitely missed it in the docs. It would be great if this were added. It was a couple weeks ago when I ran into this, and I can't remember if I was running an update or delete, but I have a feeling it was a delete and almost accidentally emptied the table.

[Mike Bayer]

there may have been reasons other than backwards compat that this is not present. at the very least, we'd probably need to get #1653 in as the single-inh discriminator uses IN. One aspect here is that since we don't do the "joined" inheritance setup, we omit the single as well since the "spirit" of query.update() / query.delete() is that inheritance situations require special attention; having the single inh criteria be automatic here would conflict with that.